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Carbon dioxide () is an important trace gas in Earth's atmosphere currently constituting about 0.04% (400 parts per million) of the atmosphere. Despite its relatively small concentration, is a potent greenhouse gas and plays a vital role in regulating Earth's surface temperature through radiative forcing and the greenhouse effect.〔 absorbs and emits infrared radiation at wavelengths of 4.26 µm (asymmetric stretching vibrational mode) and 14.99 µm (bending vibrational mode).〕 Reconstructions show that concentrations of in the atmosphere have varied, ranging from as high as 7,000 parts per million during the Cambrian period about 500 million years ago to as low as 180 parts per million during the Quaternary glaciation of the last two million years. Carbon dioxide is an integral part of the carbon cycle, a biogeochemical cycle in which carbon is exchanged between the Earth's oceans, soil, rocks and biosphere. The present biosphere of Earth is dependent on atmospheric for its existence. Plants and other photoautotrophs use solar energy to synthesize carbohydrate from atmospheric carbon dioxide and water by photosynthesis. Carbohydrate derived from consumption of plants as food is the primary source of energy and carbon compounds in almost all other organisms. The current episode of global warming is attributed primarily to increasing industrial emissions into Earth's atmosphere. The global annual mean concentration of in the atmosphere has increased markedly since the Industrial Revolution, from 280 ppm to 400 ppm as of 2015.〔(【引用サイトリンク】url=ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_annmean_gl.txt )〕 The present concentration is the highest in the past 800,000 years and likely the highest in the past 20 million years.〔(Climate Change 2001: The Scientific Basis )〕 The increase has been caused by anthropogenic sources, particularly the burning of fossil fuels and deforestation. The daily average concentration of atmospheric CO2 at Mauna Loa first exceeded 400 ppm on 10 May 2013. It is currently rising at a rate of approximately 2 ppm/year and accelerating. An estimated 30–40% of the released by humans into the atmosphere dissolves into oceans, rivers and lakes. which contributes to ocean acidification. ==Current concentration== Over the past 400,000 years, concentrations have shown several cycles of variation from about 180 parts per million during the deep glaciations of the Holocene and Pleistocene to 280 parts per million during the interglacial periods. Following the start of the Industrial Revolution, atmospheric concentration has increased to 400 parts per million and continues to increase. This has caused the phenomenon of global warming which is mostly attributed to human emissions.〔 (Climate Change 2013 Working Group 1 website. )〕 The global average concentration of in Earth's atmosphere is currently about 0.04%,〔Earth System Research Laboratory Pablo es lindo Global Monitoring Division>〕 or 400 parts per million by volume (ppm).〔 There is an annual fluctuation of about 3–9 ppm which is negatively correlated with the Northern Hemisphere's growing season. The Northern Hemisphere dominates the annual cycle of concentration because it has much greater land area and plant biomass than the Southern Hemisphere. Concentrations reach a peak in May as the Northern Hemisphere spring greenup begins and decline to a minimum in October when the quantity of biomass undergoing photosynthesis is greatest.〔(【引用サイトリンク】publisher=Carbon Dioxide Information Analysis Center (CDIAC) )〕 Because global warming is attributed primarily to increasing atmospheric concentrations, scientists closely monitor atmospheric concentrations and their impact on the present-day biosphere. At the scientific recording station in Mauna Loa, the concentration reached 400 ppm for the first time in May 2013,〔 although this concentration had already been reached in the Arctic in June 2012. Sir Brian Hoskins of the Royal Society said that the 400 ppm milestone should "jolt governments into action." The ''National Geographic'' noted that the concentration of carbon dioxide in the atmosphere is this high "for the first time in 55 years of measurement—and probably more than 3 million years of Earth history," and according to the global monitoring director at the National Oceanic and Atmospheric Administration's Earth System Research Lab, "it's just a reminder to everybody that we haven't fixed this, and we're still in trouble." The current concentration may be the highest in 20 million years.〔(Climate Change 2001: The Scientific Basis )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Carbon dioxide in Earth's atmosphere」の詳細全文を読む スポンサード リンク
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